a mi me funciona...
Código PHP:
<html>
...
<script>
inputs = document.getElementsByTagName('input');
function lala()
{
for (i=0;i<inputs.length;i++)
{
if (inputs[i].id == "mi_id")
{
inputs[i].onmouseover = new Function("MiFuncion()");
}
}
}
function MiFuncion()
{
...
}
</script>
<body onload="lala()">
...
<form>
...
<input type = "text" id="mi_id" name = "campo1" ...>
<input type = "text" id="mi_id" name = "campo2" ...>
...
</form>
</body>
...
</html>